The present invention relates to liquid filters for water and the like and, more particularly to a liquid filter cartidge comprising a hollow cylindrical body having top and bottom bulkheads closing top and bottom ends, respectively, thereof, the body having a plurality of peripheral input openings through the body into the top chamber for the introduction of liquid into the filter, the body further including a plurality of spaced inward-facing peripheral ridges on the inner surface of the body for preventing laminar flow of liquid therethrough adjacent the inner walls of the body; a top intermediate bulkhead disposed in spaced relationship with the top bulkhead to form a top chamber therebetween, the top intermediate bulkhead having passageways therethrough for the passage of liquid; a bottom intermediate bulkhead disposed in spaced relationship with the bottom bulkhead to form a bottom chamber therebetween, the top and bottom intermediate bulkheads being spaced from one another to form a middle chamber therebetween within the body, the bottom intermediate bulkhead having a passageway disposed about the outer periphery thereof for the passage of liquid; a quantity of activated granular adsorbent material disposed within the middle chamber; top filter means disposed between the peripheral input openings and the grandular material for initially filtering liquid coming into the body and for preventing backflow of the granular material out of the middle chamber into the peripheral input openings, the top filter means comprising an annular pad of compressed fibrous material impregnated with a quantity of carbon material disposed within the top chamber between the top bulkhead and the top intermediate bulkhead; an outlet conduit axially disposed within the body communicating with the bottom chamber through the bottom intermediate bulkhead on one end, the other end of the outlet conduit passing upward through the top intermediate bulkhead and the top bulkhead and being the outlet for filtered liquid from the filter cartridge, the conduit including a plurality of spaced outward-facing peripheral ridges on the outer surface thereof for preventing laminar flow of liquid therealong adjacent the conduit; and, bottom filter means disposed between the passageway of the bottom intermediate bulkhead and the point of communication of the outlet conduit therethrough on the one end for preventing outflow of the granular material from the middle chamber into the outlet conduit, the bottom filter means comprising an annular pad of compressed fibrous material impregnated with a quantity of carbon material disposed within the bottom chamber between the bottom bulkhead and the bottom intermediate bulkhead, whereby liquid entering the filter passes radially inward through the top filter before passing through the passageways in the top intermediate bulkhead to enter the middle chamber, and liquid exiting the middle chamber and entering the bottom chamber passes radially inward through the bottom filter before entering the outlet conduit.
Cartridge type liquid filters are well known in the art, particularly for residential and light commercial use in the treating of water for drinking and other uses. As far as is known by the applicant herein, all of the disposable granular activated carbon (GAC) units commercially available today for such use basically consist of plastic canisters filled with activated carbon granules, normally either 14.times.40 or 20.times.50 mesh. Typically, fibrous pad arrangements are used to pre-filter the incoming water and post-filter the treated water which normally contains some content of carbon "fines". Typical structural arrangements for prior art GAC filters are shown in simplified form in FIGS. 1-3. Examples corresponding to FIGS. 1-3 can be found in U.S. Pat. Nos. 4,104,170 by Nedza, 4,350,590 by Robinson and 4,131,544 by Elahi as well as 4,032,457 of the Applicant herein and 183,599 by Sinclaire.
Turning first to FIG. 1, a filter assembly, generally indicated as 10, is shown in simplified form. Filter assembly 10 comprises an outer filter housing 12 in which a replaceable filter cartridge 14 is disposed. The filter housing 12 can be opened and reclosed to replace the filter cartridge 14 if an when necessary. Housing 12 has an inlet pipe 16 in its sidewalls into which water, as symbolized by the arrows 18, enters. The inlet pipe 16 can be located as desired, as long as it introduces the water into the area 20 surrounding the filter cartridge 14. An outer pipe 22 also communicates through the endwall and provides an outlet for the filtered water exiting the filter assembly 10. Outlet pipe typically has a nipple 24 extending into the housing 12 onto which the filter cartridge is press fit. The filter cartridge comprises a closed cylindrical body 26 having a plurality of peripheral holes 28 in the sidewalls through which water 18 can enter. The body 26 if filled with granular activated charcoal 30 of the type previous described. A post-filter pad 32 is provided adjacent the opening of the outlet pipe 22 so as to filter out any charcoal fines. As shown by the various water arrows 18, the water to be filtered enters the area 20 through the inlet pipe 16 thus surrounding the filter cartridge 14. It then passes through the holes 28, through the activated charcoal granules 30, through the post-filter pad 32, and out the outlet pipe 22.
The filter assembly 10' of FIG. 2 is quite similar to that of FIG. 1 except for the replacement of the plurality of holes 28 by a single entrance hole 34 in the bottom of the filter cartridge 14'. The hole 34, of course, contains means (not shown) for preventing the granules 30 from falling out. Again, as shown by the water arrows 18, the water enters the housing 12 through the inlet pipe 16 and surrounds the filter cartridge 14'. In this case, however, the water rises upward through the granules 30 and, theoretically, is all equally filtered thereby.
The filter cartridge 14" of FIG. 3 is a variation of the filter assembly 10' of FIG. 2. In this instance, because of the single entrance and exit holes, the outer filter housing is eliminated and the inlet pipe 16 and outlet pipe 22 are connected directly to the body 26" of the filter cartridge 14".
Generally, the prior art filters as described above are mounted vertically in the manner depicted in the drawings so that gravity will work to advantage; that is, the filtering activated charcoal granules will tend to be compacted to the bottom of the filter. Unfortunately, the natural tendencies of fluids and granules in a fluid stream tend to counter the intended manner of operation. First, the upward flow of the water 18 tends to fluidize the granules 30 causing them to move and shift in the manner of a fluid instead of maintaining their fixed and compacted positions. Thus, channels of least resistance through the granules 30 tend to form. As a result, instead of passing through a tortuous path tending to provide maximum exposure to the action of the activated charcoal of the granules 30, the water 18 tends to move along paths providing a minimum of exposure to any filtering effect. Similarly, a laminar flow region tends to form adjacent the inner walls 36 of the filter body 26, 26', 26" where the granules 30 are moved slightly away from the walls 36 and the water 18 can slip through between the walls 36 and the granules 30 with virtually no filtering action. In an attempt to prevent the above-described counter productive phenomena, various attempts have been made to create a physical downward pressure on the granules. For example, many manufacturers of such units normally incorporate some type of open cell, resilient foam at the inner top of the filter above the granules 30 to keep the carbon bed under som degree of compaction during the on-off cycle of water flow.
While there is some help in the use of foam and such, some fluidization still takes place--with an additional detrimental effect; that is, even a slight fluidization causes the granules 30 to work against one another producing additional "fines" which are small enough to slip between the larger granules 30. The process is a deteriorating one with respect to the operation of the filter. Primarily, the fines must be caught by an effective post-filter so as to prevent their entering the filtered water stream. An effective post-filter, unfortunately, also becomes fairly quickly "plugged" with the fines, resulting in, initially, reduction in performance and, ultimately, early failure with the need to replace. Consequently, post-filters in the prior art have been relatively open pored in which some fines are allowed to pass to avoid premature failure with the result that post-filters have been less than satisfactory.
Wherefore, it is the object of the present invention to provide a liquid filter of the activated granular adsorbent carbon type which provides maximum filtering effect but with corresponding long life and a minimum tendency and deteriorate.